The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Cooling fan assemblies may provide airflow to dissipate heat generated by electronic components. Cooling fan assemblies may include a motor that drives fan blades via a rotor. The speed of the rotor may be adjusted to adjust airflow and heat dissipation.
Referring now to FIG. 1, a cooling fan system 100 includes a motor 102 and a motor control module 104. The motor 102 may include a two-phase brushless direct current (DC) motor. The motor 102 may include four stator poles: pole A1 106, pole A2 108, pole B1 110, and pole B2 112. Pole A1 106 and pole A2 108 may collectively be called “pole pair A.” Pole pair A may be wound with a stator coil 114 (hereinafter “coil A 114”). Pole B1 110 and pole B2 112 may collectively be called “pole pair B.” Pole Pair B may be wound with a stator coil 115 (hereinafter “coil B 115”). The motor control module 104 may apply a voltage and/or current to coil A 114 to generate a magnetic field between pole A1 106 and pole A2 108. Applying the voltage and/or current to coil A 114 may be called “driving phase A.” The motor control module 104 may apply the voltage and/or current to coil B 115 to generate a magnetic field between pole B1 110 and pole B2 112. Applying the voltage and/or current to coil B 115 may be called “driving phase B.”
The motor 102 includes a rotor 116. The rotor 116 may include at least one permanent magnet. The motor control module 104 may drive phase A and/or phase B to actuate the rotor 116 about an axle 118. The axle 118 may mechanically couple the rotor 116 to a device. For example, the axle 118 may mechanically couple the rotor 116 to a fan 120 used to cool electronic components. While the rotor 116 in FIG. 1 rotates between the stator poles 106, 108, 110, 112, the motor 102 may include a rotor that surrounds the stator poles 106, 108, 110, 112.
The motor control module 104 may alternate between driving phase A and driving phase B to actuate the rotor 116. The motor control module 104 may drive phase A twice and drive phase B twice to rotate the rotor 116 one revolution. For example, the motor control module 104 may drive phase A, then drive phase B, then drive phase A, then drive phase B to rotate the rotor 116 one revolution.
The motor 102 may include at least one Hall-effect sensor 122 that indicates rotation of the rotor 116. For example, the Hall-effect sensor 122 may generate a pulse when a magnetic pole of the rotor 116 passes the Hall-effect sensor 122. The motor control module 104 may determine a rotational speed of the rotor 116 based on the pulses from the Hall-effect sensor 122.
Referring now to FIG. 2A, the motor 102 may be connected to a power supply that provides a power supply voltage (Vsupply). Vsupply may be connected to a common termination 154 (hereinafter “center tap 154”) of coil A 114 and coil B 115 via a diode 123. The diode 123 may protect against reverse voltage.
Transistor A 150 may connect coil A 114 to ground when a voltage is applied to a gate of transistor A 150. The power supply may provide current through coil A 114 when transistor A 150 connects coil A 114 to ground. Accordingly, the motor control module 104 may apply a voltage to transistor A 150 to drive phase A. Node voltage VA may be near ground when the motor control module 104 drives phase A.
Transistor B 152 may connect coil B 115 to ground when a voltage is applied to a gate of transistor B 152. The power supply may provide current through coil B 115 when transistor B 152 connects coil B 115 to ground. Accordingly, the motor control module 104 may apply a voltage to transistor B 152 to drive phase B. Node voltage VB may be near ground when the motor control module 104 drives phase B.
The motor control module 104 may reduce the voltage applied to transistor A 150 to turn off transistor A 150. Current may not flow through coil A 114 when transistor A 150 is turned off. The motor control module 104 may reduce the voltage applied to transistor B 152 to turn off transistor B 152. Current may not flow through coil B 115 when transistor B 152 is turned off.
Referring now to FIG. 2B, the graph illustrates driving phase A and driving phase B based on signals from the Hall-effect sensor 122. The motor control module 104 may drive the motor 102 using pulse-width modulation (PWM) driving signals when the speed of the rotor 116 is less than full speed. The PWM driving signals may include a series of driving pulses as illustrated at 155. The motor control module 104 may control a duty cycle of the driving pulses to control the speed of the rotor 116.